Power Transfer Unit and Power Transfer System

Abstract

A power transfer unit (power transfer system) includes a power supply portion, a power transfer portion, a voltage detector, a power transfer current detector, and a controller, and the controller controls a power transfer voltage value on the basis of an output voltage value detected by the voltage detector and an output current value detected by the power transfer current detector.

What is claimed is: 
     
         1 . A power transfer unit comprising:
 a power supply portion;   a power transfer portion that supplies power to an external device by power supplied by the power supply portion;   a voltage detector that detects an output voltage value of the power supply portion;   a power transfer current detector that detects an output current value of the power supply portion; and   a controller that controls a power transfer voltage value of the power supply portion, wherein   the controller controls the power transfer voltage value based on the output voltage value detected by the voltage detector and the output current value detected by the power transfer current detector.   
     
     
         2 . The power transfer unit according to  claim 1 , wherein
 the controller estimates a load resistance value of the external device based on the output voltage value and the output current value.   
     
     
         3 . The power transfer unit according to  claim 1 , wherein
 the controller:   calculates a load power value P L  of the external device by multiplying the output voltage value V t  by the output current value I t ,   estimates a load resistance value R L  of the external device by following formulas (1) to (3):
     V   t   ×I   t   =P   L    (1)
 
     V   t   =α×V   L  (α: constant)   (2)
 
     V   L   2   /P   L   =R   L    (3)
 
   in which a square of a load voltage value V L  of the external device proportional to the output voltage value V t  is divided by the load power value P L  of the external device, and   controls the power transfer voltage value such that the load resistance value R L  that is estimated becomes a prescribed load resistance value.   
     
     
         4 . The power transfer unit according to  claim 3 , wherein
 the controller estimates the load resistance value R L  of the external device based on a following formula (4):
     R   L =(1/α 2 )×( V   t   /I   t )   (4)
 
   where the output voltage value V t , the output current value I t , and a constant α are employed.   
     
     
         5 . The power transfer unit according to  claim 3 , wherein
 the controller estimates the load resistance value R L  of the external device based on a following formula (5):
     R   L =(1/(η·β 2 ))×( V   t   /I   t )   (5)
 
   where the output voltage value V t , the output current value I t , a constant β, and a power transfer efficiency value η from the power supply portion to the external device are employed.   
     
     
         6 . The power transfer unit according to  claim 2 , wherein
 the controller sets a product of the load resistance value of the external device that is estimated and the output current value as the power transfer voltage value.   
     
     
         7 . The power transfer unit according to  claim 2 , wherein
 the controller determines that a load of the external device is in an abnormal state when a load power value of the external device obtained by multiplying the output voltage value V t  by the output current value I t  is at least a prescribed power value and the load resistance value that is estimated is not more than a prescribed minimum resistance value.   
     
     
         8 . The power transfer unit according to  claim 2 , wherein
 the controller controls the output voltage value based on a previously set power transfer efficiency from the power supply portion to the external device such that the load resistance value of the external device becomes a prescribed load resistance value.   
     
     
         9 . The power transfer unit according to  claim 2 , wherein
 the power transfer portion includes a power transfer coil and a resonance capacitor connected to the power transfer coil,   the power transfer unit further comprising a coil current detector that detects a coil current value that is a current value of current that flows into the power transfer coil and the resonance capacitor, wherein   the controller estimates a load power value of the external device by multiplying the output voltage value by the output current value and determines whether or not to estimate the load resistance value of the external device based on the load power value and the coil current value.   
     
     
         10 . The power transfer unit according to  claim 9 , wherein
 the resonance capacitor is connected in series to the power transfer coil, and   the controller does not estimate the load resistance value of the external device but determines that the external device is not arranged at a prescribed arrangement position when the load power value that is estimated is not more than a prescribed power value and the coil current value is at least a prescribed current value.   
     
     
         11 . The power transfer unit according to  claim 10 , wherein
 the controller increases the power transfer voltage value when the coil current value is less than the prescribed current value.   
     
     
         12 . The power transfer unit according to  claim 2 , wherein
 the controller controls the power transfer voltage value such that the load resistance value that is estimated becomes a prescribed load resistance value, and   the prescribed load resistance value is a resistance value at which a power transfer efficiency value from the power supply portion to the external device is in the vicinity of a maximum value.   
     
     
         13 . The power transfer unit according to  claim 2 , wherein
 the controller controls the power transfer voltage value such that a load power value of the external device obtained by multiplying the output voltage value V t  by the output current value I t  is less than a prescribed power value or the load resistance value that is estimated exceeds a prescribed minimum resistance value.   
     
     
         14 . The power transfer unit according to  claim 2 , wherein
 the controller increases the power transfer voltage value when the load resistance value that is estimated is smaller than a prescribed load resistance value and reduces the power transfer voltage value when the load resistance value that is estimated is larger than the prescribed load resistance value.   
     
     
         15 . The power transfer unit according to  claim 2 , wherein
 the controller estimates the load resistance value of the external device by a table that shows a correspondence relationship between both the output voltage value and the output current value and the load resistance value of the external device.   
     
     
         16 . A power transfer system comprising:
 a power transfer unit including a power supply portion, a power transfer portion that supplies power by power supplied by the power supply portion, a voltage detector that detects an output voltage value of the power supply portion, a power transfer current detector that detects an output current value of the power supply portion, and a controller that controls a power transfer voltage value of the power supply portion; and   a receiver including a power receiving portion that receives power from the power transfer portion and a power converter that converts a voltage value of the power received by the power receiving portion to a prescribed voltage value, wherein   the controller controls the power transfer voltage value based on the output voltage value detected by the voltage detector and the output current value detected by the power transfer current detector.   
     
     
         17 . The power transfer system according to  claim 16 , wherein
 the controller estimates a load resistance value of the receiver based on the output voltage value and the output current value.   
     
     
         18 . The power transfer system according to  claim 16 , wherein
 the controller:   calculates a load power value P L  of the receiver by multiplying the output voltage value V t  by the output current value I t ,   estimates a load resistance value R L  of the receiver by following formulas (6) to (8):
     V   t   ×I   t   =P   L    (6)
 
     V   t   =α×V   L  (α: constant)   (7)
 
     V   L   2   /P   L   =R   L    (8)
 
   in which a square of a load voltage value V L  of the receiver proportional to the output voltage value V t  is divided by the load power value P L  of the receiver, and   controls the power transfer voltage value such that the load resistance value R L  that is estimated becomes a prescribed load resistance value.   
     
     
         19 . The power transfer system according to  claim 18 , wherein
 the controller estimates the load resistance value R L  of the receiver based on a following formula (9):
     R   L =(1/α 2 )×( V   t   /I   t )   (9)
 
   where the output voltage value V t , the output current value I t , and a constant α are employed.   
     
     
         20 . The power transfer system according to  claim 18 , wherein
 the controller estimates the load resistance value R L  of the receiver based on a following formula (10):
     R   L =(1/(η·β 2 ))×( V   t   /I   t )   (10)
 
   where the output voltage value V t , the output current value I t , a constant β, and a power transfer efficiency value η from the power supply portion to the receiver are employed.